The present invention relates to the field of processes for manufacturing hollow bodies of thermoplastic materials, in which a preform is first manufactured by injection before obtaining the final container during a blow forming stage.
The preform obtained by injection generally presents a tubular cylindrical body that is closed at one of its axial ends and which is extended at its other end by a neck, which is also tubular. The neck is generally injected so that it already has its final form, while the body of the preform is required to undergo a relatively significant deformation, in order to form the final container following a blow forming operation.
In order to be able to proceed to this blow forming operation, the body of the preform must be carried at a temperature that is higher than the vitreous transition temperature of the material. To that end, the preform is temperature conditioned by circulating it inside an oven. The oven has heating means formed from infrared lamps, for example, in front of which the preform is moved by a carrying device.
However, when the preform is carried inside the oven, care must be taken that the neck of the preform be heated as little as possible, to prevent it from becoming deformed, because it is already in its final form. To do this, it is known that two protection ramps can be arranged in the oven along the path of the preform, which protection ramps are placed on either side of the preform, just at the level of the boundary between its neck and its body. In this way, the ramps form a screen and the lamps can not emit rays directly toward the neck of the preform.
However, because the rays emitted by the lamps are propagated in all directions, some of the rays emitted by the lamp can reach the neck after penetrating to the interior of the preform.
Indeed, the preforms are generally held on the carrying device by a gripping device formed from a mandrel, which is engaged inside the neck of the preform, and which holds said preform by tightening against the internal face of the neck. In this case, the tightened mandrel prevents the rays that have penetrated into the interior of the preform from reaching the neck.
However, for certain applications it is advantageous not to hold the preforms by the internal face of the neck, for example in order to avoid any bacteriological contamination of that surface, if it is brought into contact with the product with which the container will be filled. This also makes it possible to eliminate any risk of scratching the internal face of the neck.
One solution to this problem consists in providing a gripping device for the bottle which cooperates with the external face of the neck of the preform. However, such an arrangement can result in the neck being heated by the rays that have penetrated into the interior of the preform, which should be avoided at any cost. This problem becomes particularly acute when the container being manufactured is a container having a neck with a large diameter, for example on the order of 80 millimeters. The cross section through which the rays pass to the interior of the preform is then particularly large.